In recent years, an organic EL (Electro Luminescence) display device has been attracting attention as a thin, light-weight, fast-response display device. The organic EL display device includes a plurality of pixel circuits arranged two-dimensionally. The pixel circuit of the organic EL display device includes an organic EL element, and a drive transistor connected in series with the organic EL element. The drive transistor controls an amount of current flowing through the organic EL element, and the organic EL element emits light at brightness in accordance with the amount of the flowing current.
In a manufacturing process, variation occurs in characteristics of elements in the pixel circuit. Furthermore, the characteristics of the elements in the pixel circuit fluctuate with a passage of time. For example, characteristics of the drive transistor individually degrade in accordance with light emission brightness and light emission time. The same holds true for characteristics of the organic EL element. Thus, even when a same voltage is applied to gate terminals of the drive transistors, variation occurs in the light emission brightness of the organic EL elements.
Thus, in order to perform high image quality display in the organic EL display device, there is known a method in which a video signal is corrected so that variation and fluctuation of the characteristics of the organic EL element and the drive transistor are compensated. For example, Patent Document 1 discloses an organic EL display device for compensating for the fluctuation of the characteristics of the organic EL element by measuring a voltage between terminals of the organic EL element when a detection current flows through the organic EL element, and correcting a video signal based on the measured voltage.
In relation to the present invention, Patent Document 2 discloses an organic EL display device including a sensing unit shown in FIG. 15 in order to obtain a threshold voltage of the drive transistor and degradation information of the organic EL element. In FIG. 15, an amplification unit 91 amplifies a voltage of a node in the pixel circuit. An error compensation unit 92 includes two operational amplifiers, four capacitors C1 to C4, and 12 switches. The error compensation unit 92 compensates for an error component of elements included in the amplification unit 91 and the error compensation unit 92, for example, by controlling the switches to alternately store a voltage in the capacitors C3, C4.